Effect of NADPH oxidase inhibition on the expression of kidney injury molecule and calcium oxalate crystal deposition in hydroxy-L-proline-induced hyperoxaluria in the male Sprague-Dawley rats

The Protective Role of Dietary Polyphenols in Urolithiasis: Insights into Antioxidant Effects and Mechanisms of Action

Urolithiasis is a common urological disease with increasing prevalence and high recurrence rates around the world. Numerous studies have indicated reactive oxygen species (ROS) and oxidative stress (OS) were crucial pathogenic factors in stone formation. Dietary polyphenols are a large group of natural antioxidant compounds widely distributed in plant-based foods and beverages. Their diverse health benefits have attracted growing scientific attention in recent decades. Many literatures have reported the effectiveness of dietary polyphenols against stone formation. The antiurolithiatic mechanisms of polyphenols have been explained by their antioxidant potential to scavenge free radicals and ROS, modulate the expression and the activity of endogenous antioxidant and prooxidant enzymes, regulate signaling pathways associated with OS, and maintain cell morphology and function. In this review, we first describe OS and its pathogenic effects in urolithiasis and summarize the classification and sources of dietary polyphenols. Then, we focus on the current evidence defining their antioxidant potential against stone formation and put forward challenges and future perspectives of dietary polyphenols. To conclude, dietary polyphenols offer potential applications in the treatment and prevention of urolithiasis.

Proposal for pathogenesis-based treatment options to reduce calcium oxalate stone recurrence

Objective

Prevalence of kidney stone disease continues to increase globally with recurrence rates between 30% and 50% despite technological and scientific advances. Reduction in recurrence would improve patient outcomes and reduce cost and stone morbidities. Our objective was to review results of experimental studies performed to determine the efficacy of readily available compounds that can be used to prevent recurrence.

Methods

All relevant literature up to October 2020, listed in PubMed is reviewed.

Results

Clinical guidelines endorse the use of evidence-based medications, such as alkaline agents and thiazides, to reduce urinary mineral supersaturation and recurrence. However, there may be additional steps during stone pathogenesis where medications could moderate stone risk. Idiopathic calcium oxalate stones grow attached to Randall's plaques or plugs. Results of clinical and experimental studies suggest involvement of reactive oxygen species and oxidative stress in the formation of both the plaques and plugs. The renin-angiotensin-aldosterone system (RAAS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, mitochondria, and NOD-like receptor pyrin domain containing-3 (NLRP3) inflammasome have all been implicated at specific steps during stone pathogenesis in animal models.

Conclusion

In addition to supersaturation-reducing therapies, the use of anti-oxidants, free radical scavengers, and inhibitors of NADPH oxidase, NLRP3 inflammasome, and RAAS may prove beneficial for stone prevention. Compounds such as statins and angiotensin converting enzyme inhibitors are already in use as therapeutics for hypertension and cardio-vascular disease and have previously shown to reduce calcium oxalate nephrolithiasis in rats. Although clinical evidence for their use in stone prevention in humans is limited, experimental data support they be considered along with standard evidence-based medications and clinical expertise when patients are being counselled for stone prevention.

Metabolic changes in kidney stone disease

Kidney stone disease (KSD) is one of the earliest medical diseases known, but the mechanism of its formation and metabolic changes remain unclear. The formation of kidney stones is a extensive and complicated process, which is regulated by metabolic changes in various substances. In this manuscript, we summarized the progress of research on metabolic changes in kidney stone disease and discuss the valuable role of some new potential targets. We reviewed the influence of metabolism of some common substances on stone formation, such as the regulation of oxalate, the release of reactive oxygen species (ROS), macrophage polarization, the levels of hormones, and the alternation of other substances. New insights into changes in substance metabolism changes in kidney stone disease, as well as emerging research techniques, will provide new directions in the treatment of stones. Reviewing the great progress that has been made in this field will help to improve the understanding by urologists, nephrologists, and health care providers of the metabolic changes in kidney stone disease, and contribute to explore new metabolic targets for clinical therapy.

Pyrrosia petiolosa Extract Ameliorates Ethylene Glycol-Induced Urolithiasis in Rats by Inhibiting Oxidative Stress and Inflammatory Response

Objective

To study the therapeutic effect and mechanism of Pyrrosia petiolosa (P. petiolosa) extract on ethylene glycol- (EG-) induced urolithiasis in rats.

Methods

Thirty SD male rats were randomly divided into five groups (n = 6): control group, EG group, and P. petiolosa group (25 mg/kg, 50 mg/kg group, and 100 mg/kg). Biochemical testing was adopted for measuring the blood and urine parameters, as well as the level of superoxide dismutase (SOD), glutathione (GSH), and malondialdehyde acid (MDA) in kidney tissues. HE staining and ELISA were utilized to observe the histopathological changes and detect the level of IL-1β, IL-6, MCP-1, and TNF-α in the kidney tissue, respectively. And western blot was performed for checking NOX2, NOX4, TGF-β1, p-Smad3, Smad3, p-Smad2, and Smad2 protein expression level in kidney tissues.

Results

EG could significantly increase the level of blood urea nitrogen, creatinine, and Na in serum and 24-hour urinary protein, oxalate, uric acid, creatinine, calcium, and phosphorus in urine and decreased the urine volume in rats. Whereas P. petiolosa extract was able to greatly decrease the level of related parameters in serum and urine in a dose-dependent manner, but did not affect the urine pH. In addition, P. petiolosa extract notably ameliorated EG-induced renal tissue injury. Compared with the EG group, P. petiolosa extract markedly raised the level of SOD and GSH and decreased the MDA level and the expression of NOX2 and NOX4 in the kidney tissue. Moreover, P. petiolosa extract also lowered the level of IL-1β, IL-6, MCP-1, and TNF-α in EG-stimulated kidney tissue and inhibited the protein level of EG-induced TGF-β1, p-Smad3, and p-Smad2 in a concentration-dependent manner.

Conclusion

P. petiolosa extract can improve EG-induced urolithiasis in rats by inhibiting oxidative stress, inflammatory response, and the activation of TGF-β pathway.

The role of reactive oxygen species derived from different NADPH oxidase isoforms and mitochondria in oxalate-induced oxidative stress and cell injury

Hyperoxaluria is a risk factor for urolithiasis and can cause renal epithelial cell injury secondary to oxidative stress. Reactive oxygen species (ROS) produced during cell damage originate from different sources and play different roles. Here, we explored the potential sources of ROS production and investigated the role of ROS from various sources in oxalate-induced oxidative stress and cell injury in normal rat kidney-52 epithelial (NRK-52E) cells. Oxalate-induced injury was assessed by lactate dehydrogenase (LDH) release experiments. 2,7-dichlorodihydrofluorescein diacetate and mitoSOX Red were used to determine the intracellular and mitochondrial ROS (mtROS) production, respectively. The expression level of Nox4, Nox2, and p22 protein was detected by Western blotting to observe the effect of oxalate on nicotinamide adenine dinucleotide phosphate oxidase (NADPH) oxidase (Nox). Furthermore, a specific NADPH oxidase subtype inhibitor and targeted mitochondrial antioxidants were used to preliminarily identify the role of ROS from different sources in renal tubular epithelial cell injury induced by oxalate. We found that oxalate inhibited cell viability, induced LDH release, and prompted intracellular and mitochondrial ROS (mtROS) production. Oxalate also decreased the protein expression level of Nox4 and increased the protein expression level of p22. Mitochondria were also a source of ROS production. In addition, Nox2 inhibitor or mtROS scavenging prevented oxalate-induced cell injury, reversed by an inhibitor of Nox4/1. We concluded that ROS from different sources might play different roles in oxalate-induced renal tubular epithelial cell injury. We also identified new potential targets for preventing or alleviating oxalate-induced renal tubular epithelial cell injury.

Graphic abstract

The Antiviral Roles of Hydrogen Sulfide by Blocking the Interaction between SARS-CoV-2 and Its Potential Cell Surface Receptors

The ongoing coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is posing a great threat to the global economy and public health security. Together with the acknowledged angiotensin-converting enzyme 2, glucose-regulated protein 78, transferrin receptor, AXL, kidney injury molecule-1, and neuropilin 1 are also identified as potential receptors to mediate SARS-CoV-2 infection. Therefore, how to inhibit or delay the binding of SARS-CoV-2 with the abovementioned receptors is a key step for the prevention and treatment of COVID-19. As the third gasotransmitter, hydrogen sulfide (H2S) plays an important role in many physiological and pathophysiological processes. Recently, survivors were reported to have significantly higher H2S levels in COVID-19 patients, and mortality was significantly greater among patients with decreased H2S levels. Considering that the beneficial role of H2S against COVID-19 and COVID-19-induced comorbidities and multiorgan damage has been well-examined and reported in some excellent reviews, this review will discuss the recent findings on the potential receptors of SARS-CoV-2 and how H2S modulates the above receptors, in turn blocking SARS-CoV-2 entry into host cells.

Randall's plaque and calcium oxalate stone formation: role for immunity and inflammation

Idiopathic calcium oxalate (CaOx) stones often develop attached to Randall's plaque present on kidney papillary surfaces. Similar to the plaques formed during vascular calcification, Randall's plaques consist of calcium phosphate crystals mixed with an organic matrix that is rich in proteins, such as inter-α-trypsin inhibitor, as well as lipids, and includes membrane-bound vesicles or exosomes, collagen fibres and other components of the extracellular matrix. Kidney tissue surrounding Randall's plaques is associated with the presence of classically activated, pro-inflammatory macrophages (also termed M1) and downregulation of alternatively activated, anti-inflammatory macrophages (also termed M2). In animal models, crystal deposition in the kidneys has been associated with the production of reactive oxygen species, inflammasome activation and increased expression of molecules implicated in the inflammatory cascade, including osteopontin, matrix Gla protein and fetuin A (also known as α2-HS-glycoprotein). Many of these molecules, including osteopontin and matrix Gla protein, are well known inhibitors of vascular calcification. We propose that conditions of urine supersaturation promote kidney damage by inducing the production of reactive oxygen species and oxidative stress, and that the ensuing inflammatory immune response promotes Randall's plaque initiation and calcium stone formation.

Calcium-sensing receptor promotes calcium oxalate crystal adhesion and renal injury in Wistar rats by promoting ROS production and subsequent regulation of PS ectropion, OPN, KIM-1, and ERK expression

OBJECTIVES

To explore the mechanism of calcium-sensing receptors (CaSRs) during the development of nephrolithiasis.

MATERIALS AND METHODS

Wistar rats were treated with ethylene glycol to induce calcium oxalate crystallization, and gadolinium chloride (GdCl₃, an agonist of CaSR) and NPS 2390 (an antagonist of CaSR) were added. Oxidative stress (OS) and calcium oxalate crystals in the kidney were observed. CaSR expression and the expression of extracellular signal-regulated protein kinase (ERK), OPN, and KIM-1 were determined by western blotting. In addition, renal tubular epithelial cells were isolated from the kidney to observe phosphatidylserine (PS) ectropion using flow cytometric analysis. Various biochemical parameters were assessed in serum and urine at the end of the experiment.

RESULTS

Calcium oxalate increased OS, crystal adhesion, PS ectropion, and the expression of CaSR and ERK, OPN, and KIM-1 in vivo. In addition, lower levels of urine citrate as well as increased serum creatinine and urea levels were observed after treatment with calcium oxalate (p < .05). Compared with calcium oxalate treatment alone, the above deleterious changes were further significantly confirmed by GdCl₃ but were reversed by NPS-2390. However, urine calcium excretion was decreased after ethylene glycol treatment but was significantly reduced by NPS 2390 and increased by GdCl₃ (p < .05).

CONCLUSIONS

The results suggest that CaSR might play significant roles in the induction of nephrolithiasis in rats by regulating reactive oxygen species (ROS) and PS ectropion and the composition of urine, OPN, KIM-1, and ERK expression.

A different perspective on the filtration barrier after kidney stone formation: An immunohistochemical and biochemical study

The aim of this study is to investigate whether the filtration barrier is affected by experimental kidney stone formation. Thirty-two rats divided into 4 equally groups (n = 8) at random. Group I control; Group II 1% ethylene glycol; Group III 1% Ethylene glycol + 0.25% Ammonium chloride; Group IV 1% Ethylene glycol + 0.5% Ammonium chloride group. Tissues applied hematoxylin-eosin, periodic-acid-Schiff, Pizzolato's staining. Immunohistochemically stained with integrin α3β1, type IV collagen, laminin, nephrin, CD2-associated protein (CD2AP) and podocin to show the filtration barrier structure. The TUNEL method was used for apoptosis. The amount of calcium, magnesium, creatinine and uric acid in urine and blood samples, also urine microprotein determined. Stones were formed in all experimental groups. Urine calcium, creatinine, uric acid levels decreased, magnesium levels were not changed. No statistically significant change was observed in blood serum results and TUNEL analysis. Immunohistochemical results showed an increase in nephrin, podocin, CD2AP, laminin and a decrease in integrin α3β1 and type IV collagen. Consequently, there is an increase in the expression densities of the proteins incorporated in the structure to prevent loss of functionality in the cellular part supporting the structure against a weakening of the basement membrane structure in the glomerular structure in which urine is filtered.

Oxalate-Degrading Bacillus subtilis Mitigates Urolithiasis in a Drosophila melanogaster Model

Kidney stone disease is a morbid condition that is increasing in prevalence, with few nonsurgical treatment options. The majority of stones are composed of calcium oxalate. Unlike humans, some microbes can break down oxalate, suggesting that microbial therapeutics may provide a novel treatment for kidney stone patients. This study demonstrated that Bacillus subtilis 168 (BS168) decreased stone burden, improved health, and complemented the microbiota in a Drosophila melanogaster urolithiasis model, while not exacerbating calcium oxalate aggregation or adhesion to renal cells in vitro. These results identify this bacterium as a candidate for ameliorating stone formation; given that other strains of B. subtilis are components of fermented foods and are used as probiotics for digestive health, strain 168 warrants testing in humans. With the severe burden that recurrent kidney stone disease imposes on patients and the health care system, this microbial therapeutic approach could provide an inexpensive therapeutic adjunct.

Kidney stones affect nearly 10% of the population in North America and are associated with high morbidity and recurrence, yet novel prevention strategies are lacking. Recent evidence suggests that the human gut microbiota can influence the development of nephrolithiasis, although clinical trials have been limited and inconclusive in determining the potential for microbially based interventions. Here, we used an established Drosophila melanogaster model of urolithiasis as a high-throughput screening platform for evaluation of the therapeutic potential of oxalate-degrading bacteria in calcium oxalate (CaOx) nephrolithiasis. The results demonstrated that Bacillus subtilis 168 (BS168) is a promising candidate based on its preferential growth in high oxalate concentrations, its ability to stably colonize the D. melanogaster intestinal tract for as long as 5 days, and its prevention of oxalate-induced microbiota dysbiosis. Single-dose BS168 supplementation exerted beneficial effects on D. melanogaster for as long as 14 days, decreasing stone burden in dissected Malpighian tubules and fecal excreta while increasing survival and behavioral markers of health over those of nonsupplemented lithogenic controls. These findings were complemented by in vitro experiments using the established MDCK renal cell line, which demonstrated that BS168 pretreatment prevented increased CaOx crystal adhesion and aggregation. Taking our results together, this study supports the notion that BS168 can functionally reduce CaOx stone burden in vivo through its capacity for oxalate degradation. Given the favorable safety profile of many B. subtilis strains already used as digestive aids and in fermented foods, these findings suggest that BS168 could represent a novel therapeutic adjunct to reduce the incidence of recurrent CaOx nephrolithiasis in high-risk patients.

IMPORTANCE Kidney stone disease is a morbid condition that is increasing in prevalence, with few nonsurgical treatment options. The majority of stones are composed of calcium oxalate. Unlike humans, some microbes can break down oxalate, suggesting that microbial therapeutics may provide a novel treatment for kidney stone patients. This study demonstrated that Bacillus subtilis 168 (BS168) decreased stone burden, improved health, and complemented the microbiota in a Drosophila melanogaster urolithiasis model, while not exacerbating calcium oxalate aggregation or adhesion to renal cells in vitro. These results identify this bacterium as a candidate for ameliorating stone formation; given that other strains of B. subtilis are components of fermented foods and are used as probiotics for digestive health, strain 168 warrants testing in humans. With the severe burden that recurrent kidney stone disease imposes on patients and the health care system, this microbial therapeutic approach could provide an inexpensive therapeutic adjunct.

Comprehensive study of altered proteomic landscape in proximal renal tubular epithelial cells in response to calcium oxalate monohydrate crystals

Background

Calcium oxalate monohydrate (COM), the major crystalline composition of most kidney stones, induces inflammatory infiltration and injures in renal tubular cells. However, the mechanism of COM-induced toxic effects in renal tubular cells remain ambiguous. The present study aimed to investigate the potential changes in proteomic landscape of proximal renal tubular cells in response to the stimulation of COM crystals.

Methods

Clinical kidney stone samples were collected and characterized by a stone component analyzer. Three COM-enriched samples were applied to treat human proximal tubular epithelial cells HK-2. The proteomic landscape of COM-crystal treated HK-2 cells was screened by TMT-labeled quantitative proteomics analysis. The differentially expressed proteins (DEPs) were identified by pair-wise analysis. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of DEPs were performed. Protein interaction networks were identified by STRING database.

Results

The data of TMT-labeled quantitative proteomic analysis showed that a total of 1141 proteins were differentially expressed in HK-2 cells, of which 699 were up-regulated and 442 were down-regulated. Functional characterization by KEGG, along with GO enrichments, suggests that the DEPs are mainly involved in cellular components and cellular processes, including regulation of actin cytoskeleton, tight junction and focal adhesion. 3 high-degree hub nodes, CFL1, ACTN and MYH9 were identified by STRING analysis.

Conclusion

These results suggested that calcium oxalate crystal has a significant effect on protein expression profile in human proximal renal tubular epithelial cells.

Melatonin inhibits oxalate-induced endoplasmic reticulum stress and apoptosis in HK-2 cells by activating the AMPK pathway

Background: Deposition of various crystal and organic substances in the kidney can lead to kidney stone formation. Melatonin is an effective endogenous antioxidant that can prevent crystalluria and kidney damage due to crystal formation and aggregation. In this study, we investigated the mechanism by which melatonin inhibits endoplasmic reticulum (ER) stress and apoptosis. Methods: We treated HK-2 cells with oxalate to establish an in vitro kidney stone model, and treated these cells with different concentrations of melatonin (0, 5, 10, 20 μmol/L) and the AMP-activated protein kinase (AMPK) inhibitor Compound C. We measured levels of stress response markers including reactive oxygen species (ROS), lactate dehydrogenase (LDH), glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT), and factors in the stress response pathway, such as ATF6, GRP78, DDIT3, PERK, p-PERK, IRE1, p-IRE1, XBP1s, AMPK, and p-AMPK, using real time-PCR, western blot, and immunofluorescence analyzes. We measured mitochondrial membrane potential and caspases-3 activity using the CCK8, enzyme-linked immunosorbent, and flow cytometry assays to assess HK-2 cell viability and apoptosis. Results: Melatonin improved the total antioxidant capacity (T-AOC) of the HK-2 cells, as evidenced by the dose-dependent reduction in apoptosis, ROS levels, and protein expression of ATF6, GRP78, DDIT3, p-PERK, p-IRE1, XBP1s, caspase-12, cleaved caspase-3 and cleaved caspase-9. Addition of the AMPK inhibitor, Compound C, partially reversed the protective effect of melatonin. Conclusion: Our study revealed that the protective effects of melatonin on oxalate-induced ER stress and apoptosis is partly dependent on AMPK activation in HK-2 cells. These findings provide insight into the prevention and treatment of kidney stones.

Antiurolithiatic effects of pentacyclic triterpenes: The distance traveled from therapeutic aspects

Globally, approximately 12% of the population is inflicted by various types of urolithiasis. Standard treatments are available both to avert and treat urolithiasis, but with significant adverse side effects. Pentacyclic triterpenes represent a group of naturally occurring compounds which holds immense potential as therapeutic for treating kidney stone. This review aims to provide an integrative description on how pentacyclic triterpenes can effectively treat calcium oxalate urolithiasis through various mechanisms such as antioxidant, anti-inflammatory, diuretic, and angiotensin-converting enzyme inhibition. Some of the pentacylic triterpenes which shows promising activities include lupeol, oleanolic acid, betulin, and taraxasterol. Moreover, future perspectives in the development of pentacyclic triterpenes in formulations/drugs for urinary stone prevention are highlighted. It is anticipated that compiled information would serve as a scientific baseline to advocate further investigations on the potential of pentacyclic triterpenes in urolithiasis remediation.

Oxidative stress and endoplasmic stress in calcium oxalate stone disease: the chicken or the egg?

Crystal modulators play a significant role in the formation of calcium oxalate stone disease. When renal cells are subjected to oxalate stress, the loss in cell integrity leads to exposure of multiple proteins that assist and/or inhibit crystal attachment and retention. Contact between oxalate and calcium oxalate with urothelium proves fatal to cells as a result of reactive oxygen species generation and onset of oxidative stress. Hence, as a therapeutic strategy it was hypothesised that supplementation of antioxidants would suffice. On the contrary to popular belief, the detection of oxalate induced endoplasmic reticulum mediated apoptosis proved the ineffectiveness of antioxidant therapy alone. Thus, the inadequacy of antioxidant supplementation in oxalate stress invoked the presence of an alternative pathway for the induction of kidney fibrosis in hyperoxaluric rats. In addition to settling this query, the link between oxidative stress and ER stress is not well understood, especially in urolithiasis.

Effect of M2 Macrophages on Injury and Apoptosis of Renal Tubular Epithelial Cells Induced by Calcium Oxalate Crystals

Background: M2 macrophages have important roles in diseases such as tumours, cardiovascular diseases and renal diseases. This study aimed to determine the effects and protective mechanism of M2 macrophages against oxidative stress injury and apoptosis induced by calcium oxalate crystals (CaOx) in renal tubular epithelial cells (HK-2) under coculture conditions. Methods: THP-1 cells were induced to differentiate into M2 macrophages by using phorbol-12-myristate-13-acetate, IL-4 and IL-13. Morphological features were observed by microscopy. Phenotypic markers were identified by reverse transcription-polymerase chain reaction, Western blot and enzyme-linked immunosorbent assay (ELISA). HK-2 cells were treated with 0.5 mg/mL CaOx crystals and co-cultured with M2 macrophages or apocynin. The viability of HK-2 cells was detected by CCK-8 assay. The lactate dehydrogenase (LDH) activity of HK-2 cells was analysed using a microplate reader. The apoptosis of HK-2 cells was examined by flow cytometry and Hoechst 33258 staining. Reactive oxygen species (ROS) expression and mitochondrial membrane potential in HK-2 cells were detected by a fluorescence microplate reader. Western blot analysis was conducted to detect the expression of p47phox, Bcl-2, cleaved caspase-3, cytochrome c, p38 MAPK, phospho-p38 MAPK, Akt and phospho-Akt. Results: The results of morphology, reverse transcription-polymerase chain reaction, Western blot and ELISA showed that THP-1 cells were successfully polarised to M2 macrophages. The results of co-culture suggested that M2 macrophages or apocynin significantly increased the cell viability and decreased the LDH activity and apoptosis rate after HK-2 cells were challenged with CaOx crystals. The expression of the p47phox protein and the concentration of ROS were reduced, the release of mitochondrial membrane potential and the expression of the Bcl-2 protein were upregulated and the protein expression of cleaved caspase-3 and cytochrome c was downregulated. The expression of the phosphorylated form of p38 MAPK increased. Under coculture conditions with M2 macrophages, the Akt protein of HK-2 cells treated with CaOx crystals was dephosphorylated, but the phosphorylated form of Akt was not reduced by apocynin. Conclusions: M2 macrophages reduced the oxidative stress injury and apoptosis of HK-2 cells by downregulating the activation of NADPH oxidase, reducing the production of ROS, inhibiting the phosphorylation of p38 MAPK and enhancing the phosphorylation of Akt. We have revealed one of the possible mechanisms by which M2 macrophages reduce the formation of kidney stones.

Efficacy of Obcordata A from Aspidopterys obcordata on Kidney Stones by Inhibiting NOX4 Expression

Obcordata A (OA) is a polyoxypregnane glycoside derived from the Dai medicine Aspidopterys obcordata vines. This study aims to investigate the efficacy of OA on renal tubular epithelial cells exposed to calcium oxalate crystals. We incubated renal tubular cells with 28 μg·cm2 calcium oxalate crystals for 24 h with and without OA, GKT137831, phorbol-12-myristate-13-acetate (PMA), and tocopherol. The MTT [3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, microscopic examination, flow cytometry, and immunofluorescence staining revealed that calcium oxalate crystals decreased cell viability and elevated reactive oxygen species (ROS) levels. OA, GKT137831, and tocopherol protected cells and decreased ROS levels. However, OA did not exhibit direct DPPH scavenging ability. In addition, immunoblotting illustrated that OA inhibited the NOX4 (nicotinamide adenine dinucleotide phosphate oxidases 4) expression and downregulated the protein expression in the NOX4/ROS/p38 MAPK (p38 mitogen-activated protein kinase) pathway. The findings suggest that the cytoprotective and antioxidant effects of OA can be blocked by the NOX4 agonist PMA. In conclusion, OA could be used as a NOX4 inhibitor to prevent kidney stones.

LncRNA-miRNA-mRNA expression variation profile in the urine of calcium oxalate stone patients

Background

To explore long-non-coding RNA (lncRNA), microRNA (miRNA) and messenger RNA (mRNA) expression profiles and their biological functions in the urine samples in calcium oxalate (CaOx) patients.

Methods

Five CaOx kidney stone patients were recruited in CaOx stone group and six healthy people were included as control group, whose midstream morning urine was collected before the patients were given any medicine on admission. After total RNA was extracted from urine, microarray of miRNA, mRNA and lncRNA were applied to explore their expression variation. Gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to reveal the gene functions of the dysregulated lncRNA-associated competing endogenous RNA (ceRNA) network. Quantitative real-time PCR were performed on HK-2 cells treated with sodium oxalate (NaOx) to further screen out the differentially expression profiles of these RNAs.

Results

A total of nine miRNAs, 883 mRNAs and 1002 lncRNAs were differentially expressed in urine of CaOx patients compared with normal population. GO analysis revealed that most of mRNAs from ceRNA network were enriched in terms of respiratory burst, regulation of mitophagy, and protein kinase regulator activity. KEGG pathway analysis of these genes related to ceRNA network highlight their critical role in pentose phosphate pathway, glyoxylate and dicarboxylate metabolism, and Janus kinase/signal transducer and activator of transcription (JAK-STAT) signaling pathway. Five miRNAs (miR-6796-3p, miR-30d-5p, miR-3192–3p, miR-518b and miR-6776-3p), four mRNAs (NT5E, CDH4, CLEC14A, CCNL1) and six lncRNAs (lnc-TIGD1L2–3, lnc-KIN-1, lnc-FAM72B-4, lnc-EVI5L-1, lnc-SERPINI1–2, lnc-MB-6) from the HK-2 cells induced by NaOx were consistent with the expression changes of microarray results.

Conclusion

The differential expressed miRNAs, mRNAs and lncRNAs may be associated with numerous variations of the signaling pathways or regulation of metabolism and kinase activity, providing potential biomarkers for early diagnosis of urolithiasis and new basis for further research of urolithiasis mechanism.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0502-y) contains supplementary material, which is available to authorized users.

The Protective Roles of Estrogen Receptor β in Renal Calcium Oxalate Crystal Formation via Reducing the Liver Oxalate Biosynthesis and Renal Oxidative Stress-Mediated Cell Injury

Females develop kidney stones less frequently than males do. However, it is unclear if this gender difference is related to altered estrogen/estrogen receptor (ER) signaling. Here, we found that ER beta (ERβ) signals could suppress hepatic oxalate biosynthesis via transcriptional upregulation of the glyoxylate aminotransferase (AGT1) expression. Results from multiple in vitro renal cell lines also found that ERβ could function via suppressing the oxalate-induced injury through increasing the reactive oxygen species (ROS) production that led to a decrease of the renal calcium oxalate (CaOx) crystal deposition. Mechanism study results showed that ERβ suppressed oxalate-induced oxidative stress via transcriptional suppression of the NADPH oxidase subunit 2 (NOX2) through direct binding to the estrogen response elements (EREs) on the NOX2 5′ promoter. We further applied two in vivo mouse models with glyoxylate-induced renal CaOx crystal deposition and one rat model with 5% hydroxyl-L-proline-induced renal CaOx crystal deposition. Our data demonstrated that mice lacking ERβ (ERβKO) as well as mice or rats treated with ERβ antagonist PHTPP had increased renal CaOx crystal deposition with increased urinary oxalate excretion and renal ROS production. Importantly, targeting ERβ-regulated NOX2 with the NADPH oxidase inhibitor, apocynin, can suppress the renal CaOx crystal deposition in the in vivo mouse model. Together, results from multiple in vitro cell lines and in vivo mouse/rat models all demonstrate that ERβ may protect against renal CaOx crystal deposition via inhibiting the hepatic oxalate biosynthesis and oxidative stress-induced renal injury.

Downregulated Expression of Solute Carrier Family 26 Member 6 in NRK-52E Cells Attenuates Oxalate-Induced Intracellular Oxidative Stress

Solute carrier family 26 member 6 (Slc26a6), which is mainly expressed in the intestines and kidneys, is a multifunctional anion transporter that is crucial in the transport of oxalate anions. This study is aimed at investigating the effect of Slc26a6 expression on oxalate-induced cell oxidation and crystal formation. Lentivirus transfection was used to upregulate or downregulate Slc26a6 expression in NRK cells. Cell viability and apoptosis, reactive oxygen species (ROS) and malondialdehyde (MDA) generation, and superoxide dismutase (SOD) activity were measured. Crystal adhesion and the cell ultrastructure were observed using light and transmission electron microscopy (TEM). Three groups of rats, normal control, lentivirus-vector, and lentivirus-small interfering RNA (lv-siRNA) groups, were used, and after lentivirus transfection, they were fed 1% ethylene glycol (EG) and 0.5% ammonium chloride (NH₄Cl) for 2 weeks. Dihydroethidium (DHE), terminal deoxynucleotidyl transferase (TdT) deoxyuridine dUTP nick-end labeling (TUNEL), and von Kossa staining were performed, and nuclear factor κB (NFκB) and osteopontin (OPN) expression were measured. In the vitro study, compared to the control group, downregulated Slc26a6 NRK cells showed alleviation of the cell viability decrease, cell apoptosis rate, ROS generation, and SOD activity decrease after oxalate treatment. Crystal adhesion and vesicles were significantly less after oxalate exposure than in the untreated controls. Rats infected with lentivirus-siRNA exhibited attenuated SOD generation, cell apoptosis, and crystal formation in the kidneys. Increased phosphorylation of NFκB and OPN was involved in the pathological process. In conclusion, the results of the present study indicate that reducing the expression of Slc26a6 in the kidney may be a potential strategy for preventing stone formation.

Albuminuria and other renal damage biomarkers detect acute kidney injury soon after acute ingestion of oxalic acid and potassium permanganate

BACKGROUND

Deliberate self-poisoning with a combination washing powder containing oxalic acid (H₂C₂O₄) and potassium permanganate (KMnO₄) is a significant medical problem in the Southern Province of Sri Lanka. Acute kidney injury (AKI) is a frequent consequence. Biomarkers for early diagnosis of nephrotoxicity could guide appropriate supportive therapies.

METHODS

We investigated the performance of three serum biomarkers and nine urinary biomarkers in 85 patients in an ongoing multicenter prospective cohort study in Sri Lanka exploring AKI following poisoning.

RESULTS

Sixty two (62/85, 73%) patients developed AKI (acute kidney injury network, AKIN, criteria). Early and rapid increases in serum creatinine (sCr) peaking on day 3 were observed in AKIN stage 2 and 3 patients. In these patients, serum cystatin C (sCysC) rose more gradually but also peaked on day 3. Biomarker concentrations (normalized to urinary creatinine) of urinary albumin (uAlbumin), clusterin (uClusterin), beta-2-microglobulin (uB2M), osteopontin (uOPN), neutrophil gelatinase-associated lipocalin (uNGAL) and kidney injury molecule-1 (uKIM-1) in the AKIN2/3 group increased above the 95th centile concentration of the healthy population. Within 8 h of ingestion, the normalized uAlbumin and sCysC predicted AKIN2/3 with respective area under receiver operating characteristic curve, AUC-ROC values, of 0.94 (95% CI 0.86-1.00) and 0.85 (95% CI 0.76-0.95).

CONCLUSIONS

Urinary albumin was the best performing AKI biomarker following ingestion of H₂C₂O₄/KMnO₄. This may reflect glomerular injury and/or proximal tubular injury. The urinary albumin concentrations observed in this study could generally be detected using albumin specific dipstick methods, easily available even in resource poor settings.

Protective effect of pentoxifylline on oxidative renal cell injury associated with renal crystal formation in a hyperoxaluric rat model

The aim of the study is to investigate the effects of pentoxifylline (PTX) on the renal tubular cell injury and stone formation in a hyperoxaluric rat model induced by ethylene glycol and its possible underlying mechanisms. The study was performed with 30 male Wistar rats and randomized into three groups of teen. The sham-control (group 1) received only drinking water orally. The EG/untreated (group 2) received drinking water containing 0.75% EG for 4 weeks orally. The EG/PTX treated (group 3) received drinking water containing 0.75% EG for 4 weeks orally and PTX. Urine and blood were collected to determine some parameters. The kidneys were also removed for histological examination. Serum and urinary parameters were significantly improved in the EG/PTX treated. In the EG/PTX-treated group, the MDA, TOS and MPO activity reduced and the TAS, SOD, CAT and GSH-Px activities were increased markedly compared with the group 2. In urine of the group 2 rats, a large number of CaOx crystals were displayed and most tubules that contained crystals were dilated and showed degeneration, necrosis, and desquamation of the lining epithelium. Only few CaOx crystals were r in EG/PTX-treated animal's urine. Mild tissue damage was observed in PTX-treated rats. iNOS expression was significantly elevated in the group 2. In contrast, in the EG/PTX-treated group, eNOS expression in renal tubular epithelial cells was increased. Current study indicates that PTX may partially reduce renal tubular injury resulting from hyperoxaluria-induced oxidative and nitrosative stress.

High expression of SLC26A6 in the kidney may contribute to renal calcification via an SLC26A6-dependent mechanism

Background

Solute-linked carrier 26 gene family 6 (SLC26A6), which is mainly expressed in intestines and kidneys, is a multifunctional anion transporter crucial in the transport of oxalate anions. This study aimed to investigate the role of kidney SLC26A6 in urolithiasis.

Methods

Patients were divided into two groups: stone formers and nonstone formers. Samples were collected from patients following nephrectomy. Lentivirus with Slc26a6 (lentivirus-Slc26a6) sequence and lentivirus with siRNA-Slc26a6 (lentivirus-siRNA-Slc26a6) sequence were transfected into rats’ kidneys respectively and Slc26a6 expression was detected using Western blot and immunohistochemical analyses. After administering ethylene glycol, oxalate concentration and prevalence of stone formation between the transgenic and control groups were measured using 24-h urine analysis and Von Kossa staining, respectively.

Results

Immunohistochemical and Western blot analyses indicated that stone formers had a significantly higher level of expression of SLC26A6 in the kidney compared with the control group. After lentivirus infection, the urinary oxalate concentration and rate of stone formation in lentivirus-Slc26a6-tranfected rats increased remarkably, while lentivirus-siRNA-Slc26a6-transfected rats showed few crystals.

Conclusion

The results showed that high expression levels of renal SLC26A6 may account for kidney stone formation. Downregulating the expression of SLC26A6 in the kidney may be a potential therapeutic target to prevent or treat urolithiasis.

Prevalence, pathophysiological mechanisms and factors affecting urolithiasis

The formation of urinary stone, urolithiasis, is one the oldest known disease affecting human throughout different civilizations and times. The exact pathophysiological mechanism of urolithiasis is not yet clear, as these calculi are of various types and too complex for simple understanding. A single theory cannot explain its formation; therefore, different theories are presented in various times for its explanation like free particle, fixed particle, Randall's plaque theory. In addition, various factors and components are identified that play an important role in the formation of these urinary calculi. In this review, composition of kidney stones, its prevalence/incidence, explanation of pathophysiological mechanisms and role of various factors; urinary pH, uric acid, parathyroid hormone, citrate, oxalate, calcium and macromolecules; osteopontin, matrix Gla protein, kidney injury molecules, urinary prothrombin fragment-1, Tamm-Horsfall protein, inter-α-inhibitors, have been discussed in detail.

Losartan Ameliorates Calcium Oxalate-Induced Elevation of Stone-Related Proteins in Renal Tubular Cells by Inhibiting NADPH Oxidase and Oxidative Stress

Calcium oxalate (CaOx) is the most common type of urinary stone. Increase of ROS and NADPH oxidase gives rise to inflammation and injury of renal tubular cells, which promotes CaOx stone formation. Recent studies have revealed that the renin-angiotensin system might play a role in kidney crystallization and ROS production. Here, we investigated the involvement of Ang II/AT1R and losartan in CaOx stone formation. NRK-52E cells were incubated with CaOx crystals, and glyoxylic acid-induced hyperoxaluric rats were treated with losartan. Oxidative stress statuses were evaluated by detection of ROS, oxidative products (8-OHdG and MDA), and antioxidant enzymes (SOD and CAT). Expression of NADPH oxidase subunits (Nox2 and Nox4), NF-κB pathway subunits (p50 and p65), and stone-related proteins such as OPN, CD44, and MCP-1 was determined by Western blotting. The results revealed upregulation of Ang II/AT1R by CaOx treatment. CaOx-induced ROS and stone-related protein upregulation were mediated by the Ang II/AT1R signaling pathway. Losartan ameliorated renal tubular cell expression of stone-related proteins and renal crystallization by inhibiting NADPH oxidase and oxidative stress. We conclude that losartan might be a promising preventive and therapeutic candidate for hyperoxaluria nephrolithiasis.

Antiurolithiatic effect of the taraxasterol on ethylene glycol induced kidney calculi in male rats

Taraxasterol is one of the important constituents of Taraxacum officinale L. (Compositae) with antioxidant potential. The present study was designed to evaluate and compare the antiurolithiatic effects of taraxasterol and potassium citrate in the ethylene glycol induced urolithiatic rat. Urolithiasis was induced by ammonium chloride and ethylene glycol in adult male rats. Taraxasterol (2, 4 and 8 mg/kg) and potassium citrate (2.5 g/kg) were treated for 33 days by gavage. Then, the animals were anesthetized and weighted and blood, urine, liver and kidney sampling were done. The kidney sections were prepared by hematoxylin & eosin staining. The liver and kidney coefficients, urine pH, calcium, magnesium, oxalate and citrate levels, serum albumin, calcium and magnesium levels, serum alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase activities, superoxide dismutase and glutathione peroxidase activities in serum, kidney and liver, number of calcium oxalate crystal deposits, score of crystal deposits, score of histopathological damages and score of inflammation in kidney sections were evaluated. The results showed that taraxasterol decreased liver and kidney coefficients (p < 0.001), serum calcium (p < 0.01) level, serum alanine aminotransferase (p < 0.001), aspartate aminotransferase (p < 0.001), lactate dehydrogenase (p < 0.05) activities, urine magnesium (p < 0.05) and oxalate (p < 0.001) levels, number of crystal deposits (p < 0.001), score of crystal deposits (p < 0.01), score of histopathological damages (p < 0.001) and score of inflammation (p < 0.01) in kidney sections, while increased urine pH (p < 0.01), calcium (p < 0.001) and citrate (p < 0.05), serum magnesium (p < 0.001) and albumin (p < 0.01) levels, superoxide dismutase and glutathione peroxidase in serum (p < 0.01), kidney (p < 0.05 and p < 0.001, respectively) and liver (p < 0.01 and p < 0.001, respectively) tissue homogenates in treated urolithiatic rats in comparison to the control urolithiatic rats. The effect of potassium citrate is the same as taraxasterol in treated urolithiatic rats. In conclusion, the effect of taraxasterol could be by improving liver function, changing serum and urine parameters, maintaining the antioxidant environment, reducing crystal deposition, excretion of small deposits from kidney and reducing the chance of them being retained in the urinary tract.

Antiurolithiatic Potential of Neeri against Calcium-Oxalate Stones by Crystallization Inhibition, Free Radicals Scavenging, and NRK-52E Cell Protection from Oxalate Injury

Background

Neeri is a well-established polyherbal formulation prescribed for renal stones by the physicians but has not been experimentally evaluated for its antiurolithiatic potential using cell-lines.

Objective

This study is aimed to scientifically substantiate the antiurolithiatic effect of Neeri extract (NRE) through calcium oxalate (CaOx) crystallization inhibition, scavenging of free radicals, and protection of renal tubular epithelial NRK-52E cells from oxalate-induced injury.

Materials and Methods

The crystallization inhibition was studied by turbidimetric assay while the free radical scavenging potential was determined for superoxide and nitric oxide (NO) radicals. The cytoprotective effect against oxalate-induced injury was assessed by estimating lactate dehydrogenase (LDH) leakage and determining cell viability using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

Results

NRE significantly inhibited the CaOx crystallization in a concentration-dependent manner and also scavenged superoxide (IC₅₀ 302.88 μg/ml) and NO (IC₅₀ 300.45 μg/ml) free radicals. It did not show any significant cytotoxicity for NRK-52E cells till the highest dose (500 μg/ml) and found to be safe. When NRK-52E cells, injured by exposing to oxalate crystals for 24 h, were treated with NRE, it appreciably prevented the cell injury in a dose-dependent manner. It significantly decreased the elevated LDH leakage toward normal range and improved renal cell viability (82.37% ± 0.87%), hence, prevented growth and retention of crystals.

Conclusion

The experimental findings concluded that Neeri is a potent antiurolithiatic formulation that inhibited CaOx crystallization and prevented tubular retention of crystals by protecting the renal cells against oxalate-induced injury as well as reducing the oxidative stress by scavenging free radicals.

SUMMARY

Neeri extract significantly (P < 0.001) inhibited the in vitro crystallization (88.11% ± 7.70%) of calcium oxalateIt reduced oxidative stress by scavenging superoxide and nitric oxide free radicalsIt significantly (P < 0.001) improved the cell viability by inhibiting the leakage of lactate dehydrogenase in a dose-dependent manner. Abbreviations used: A_c: Absorbance of control, A_t: Absorbance of test, ANOVA: Analysis of variance, CaOx: Calcium oxalate, DMEM: Dulbecco's Modified Eagle's Medium, DMSO: Dimethyl sulfoxide, EDTA: Ethylenediaminetetraacetic acid, FBS: Fetal bovine serum, INT: Iodonitrotetrazolium, LDH: Lactate dehydrogenase, M: Molar, ml: Milliliter, mM: Millimolar, MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, NAD: Nicotinamide adenine dinucleotide, NADPH: Nicotinamide adenine dinucleotide phosphate, NBT: Nitro blue tetrazolium, nm: Nanometer, NO: Nitric oxide, NRE: Neeri extract, PMS: Phenazine methosulfate, ROS: Reactive oxygen species, S_c: Slope of the graph of control, SEM: Standard error of mean, S_i: Slope of the graph with inhibitor, U/I: International unit, mg: Microgram, ml: Microliter.

Changes of Klotho protein and Klotho mRNA expression in a hydroxy-L-proline induced hyperoxaluric rat model

Klotho protein is recognized as having a renoprotective effect and is used as a biomarker for kidney injury. We investigated the level of Klotho protein in hyperoxaluria-induced kidney injury and the effects of vitamin E (Vit E) and vitamin C (Vit C) supplementation. Hyperoxaluria was induced by feeding 2% (w/v) Hydroxy-L-proline (HLP) in the drinking water for 21 days. Rats were divided into 5 groups; control (Group 1, n=7), HLP treated rats that received nothing else (Group 2, n=7), Vit E (Group 3, n=6), Vit C (Group 4, n=6) and both Vit E and Vit C (Group 5, n=7). Vit E (200 mg/kg) was injected on days 1, 6, 11 and 16, while Vit C (500 mg/kg) was given intravenously on days 1 and 11. The Klotho protein levels and oxidative status were measured. The expression level of kidney Klotho protein expression was significantly reduced by HLP-treatment, while the mRNA expression was higher (P<0.05), the plasma and kidney malondialdehyde and kidney superoxide dismutase activities were increased, and the kidney reduced glutathione and urinary total antioxidant status were decreased (P<0.05). All of these changes were ameliorated by administration of Vit E, Vit C or especially the co-administration of both. In conclusion, HLP-induced hyperoxaluria reduced the kidney Klotho protein level, which could be restored by Vit E and/or Vit C.

Transcriptional study of hyperoxaluria and calcium oxalate nephrolithiasis in male rats: Inflammatory changes are mainly associated with crystal deposition

Hyperoxaluria associated with renal deposition of calcium oxalate (CaOx) crystals causes renal injury and inflammation leading to number of diseases including chronic kidney disease (CKD). It is however, not been possible to separate the renal consequences of hyperoxaluria from that of CaOx crystal deposition. We decided to utilize ethylene glycol (EG) model where hyperoxaluria and CaOx crystal deposition can be separated in time. To test our hypothesis, male rats were made hyperoxaluric by administering EG, rats were euthanized and kidneys were extracted on day 14, when occasional crystal is seen in the kidneys and day 28, when all animals have developed renal CaOx crystal deposits. Total RNA was extracted for microarray analysis and genome wide analysis of differentially expressed genes was performed to investigate differences between hyperoxaluria and crystal induced alterations in the kidneys. Immunohistochemical and Hematoxylin and Eosin (H&E) staining was also done for macromolecules with significant role in stone formation. All EG fed rats became hyperoxaluric by day 7, showed a few crystal deposits on day 14, and had heavy crystal deposition by day 28. There were significant changes in the expression of genes encoding for NADPH Oxidases; macromolecular crystallization modulators; genes involved in inflammasome activation; and osteogenic marker genes. Results demonstrate major differences between hyperoxaluria and CaOx crystal induced changes in the kidneys. Injury and inflammation are mainly associated with crystal deposition indicating significant role played by crystal retention.

Expression of heterologous oxalate decarboxylase in HEK293 cells confers protection against oxalate induced oxidative stress as a therapeutic approach for calcium oxalate stone disease

Oxalates stimulate alterations in renal epithelial cells and thereby induce calcium oxalate (CaOx) stone formation. Bacillus subtilis YvrK gene encodes for oxalate decarboxylase (OxdC) which degrades oxalate to formate and CO₂. The present work is aimed to clone the oxdC gene in a mammalian expression vector pcDNA and transfect into Human Embryonic Kidney 293 (HEK293) cells and evaluate the oxdC expression, cell survival rate and oxalate degrading efficiency. The results indicate cell survival rate of HEK293/pcDNAOXDC cells pre-incubated with oxalate was enhanced by 28%. HEK293/pcDNAOXDC cells expressing OxdC treated with oxalate, significantly restored antioxidant activity, mitochondrial membrane potential and intracellular reactive oxygen species (ROS) generation compared with HEK293/pcDNA. Apoptotic marker caspase 3 downregulation illustrates HEK293/pcDNAOXDC cells were able to survive under oxalate-mediated oxidative stress. The findings suggest HEK293 cells expressing oxdC capable of degrading oxalate protect cells from oxidative damage and thus serve as a therapeutic option for prevention of CaOx stone disease.

MitoTEMPO Prevents Oxalate Induced Injury in NRK-52E Cells via Inhibiting Mitochondrial Dysfunction and Modulating Oxidative Stress

As one of the major risks for urolithiasis, hyperoxaluria can be caused by genetic defect or dietary intake. And high oxalate induced renal epithelial cells injury is related to oxidative stress and mitochondrial dysfunction. Here, we investigated whether MitoTEMPO, a mitochondria-targeted antioxidant, could protect against oxalate mediated injury in NRK-52E cells via inhibiting mitochondrial dysfunction and modulating oxidative stress. MitoSOX Red was used to determine mitochondrial ROS (mtROS) production. Mitochondrial membrane potential (Δψm) and quantification of ATP synthesis were measured to evaluate mitochondrial function. The protein expression of Nox4, Nox2, and p22 was also detected to explore the effect of oxalate and MitoTEMPO on NADPH oxidase. Our results revealed that pretreatment with MitoTEMPO significantly inhibited oxalate induced lactate dehydrogenase (LDH) and malondialdehyde (MDA) release and decreased oxalate induced mtROS generation. Further, MitoTEMPO pretreatment restored disruption of Δψm and decreased ATP synthesis mediated by oxalate. In addition, MitoTEMPO altered the protein expression of Nox4 and p22 and decreased the protein expression of IL-6 and osteopontin (OPN) induced by oxalate. We concluded that MitoTEMPO may be a new candidate to protect against oxalate induced kidney injury as well as urolithiasis.

Bergenin attenuates renal injury by reversing mitochondrial dysfunction in ethylene glycol induced hyperoxaluric rat model

Bergenin, isolated from Bergenia ligulata is a potent antioxidant and antilithiatic agent. Present work was designed to establish the biochemical role of bergenin on mitochondrial dysfunction in the ethylene glycol induced hyperoxaluric rat model. Bergenin was administrated at a dose of 10mg/kg body wt i.p. from 14th day of establishing the 28 days hyperoxaluria rat model. α-Tocopherol was given as positive control at a dose of 100mg/kg body wt i.p. Mitochondrial dysfunction was studied by evaluating the activities of respiratory chain complexes, mitochondrial membrane potential and reactive oxygen species. Histopathological analysis of the kidney tissue was done after Pizzolato staining. Also, expression of monocyte chemoattractant protein -1(MCP-1) and kidney injury marker protein (KIM-1) were studied and the levels of IL-1β were evaluated in kidney tissue homogenate. Mitochondrial dysfunction during stone crystallization was evident by decreased activities of electron transport chain complexes I, II and IV and augmented mitochondrial oxidative stress in hyperoxaluric rats. Bergenin treatment significantly (P<0.05) restored the activities of these complexes. Moreover, it curtailed the lipid peroxidation and up regulated antioxidant levels, ameliorating the state of mitochondrial dysfunction. The protective role of bergenin was also reinforced by reducing IL-1β production and expression of KIM-1 and MCP-1 in the renal tissue. The findings of the present study provide evidence that bergenin exerted protective effects in hyperoxaluria through mitochondrial protection that involves attenuation of oxidative stress. Hence, it presented itself as an effective remedy in combating urolithiasis.

Metformin Prevents Renal Stone Formation through an Antioxidant Mechanism In Vitro and In Vivo

Oxidative stress is a causal factor and key promoter of urolithiasis associated with renal tubular epithelium cell injury. The present study was designed to investigate the preventive effects of metformin on renal tubular cell injury induced by oxalate and stone formation in a hyperoxaluric rat model. MTT assays were carried out to determine the protection of metformin from oxalate-induced cytotoxicity. The intracellular superoxide dismutase (SOD) activities and malondialdehyde (MDA) levels were measured in vitro. Male Sprague-Dawley rats were divided into control group, ethylene glycol (EG) treated group, and EG + metformin treated group. Oxidative stress and crystal formations were evaluated in renal tissues after 8-week treatment. Metformin significantly inhibited the decrease of the viability in MDCK cells and HK-2 cells induced by oxalate. Besides, metformin markedly prevented the increased concentration of MDA and the decreased tendency of SOD in oxalate-induced MDCK cells and HK-2 cells. In vivo, the increased MDA levels and the reduction of SOD activity were detected in the EG treated group compared with controls, while these parameters reversed in the EG + metformin treated group. Kidney crystal formation in the EG + metformin treated group was decreased significantly compared with the EG treated group. Metformin suppressed urinary crystal deposit formation through renal tubular cell protection and antioxidative effects.

Urinary MCP-1、HMGB1 increased in calcium nephrolithiasis patients and the influence of hypercalciuria on the production of the two cytokines

The study aims to observe the urinary excretion of monocyte chemoattractant-1 (MCP-1) and high-mobility group box 1 (HMGB1) in patients with calcium nephrolithiasis and to determine the influence of hypercalciuria on the production of the two cytokines. 81 cases of patients with calcium nephrolithiasis (group CN) and 30 healthy controls (group C) were involved in this study. To observe the influence of urinary calcium on the excretion of those cytokines, the patients were subdivided according to their 24-h urinary calcium level: ≥4 mg/kg/day (group H) and <4 mg/kg/day (group N). MCP-1 and HMGB1 in urina sanguinis were determined for all subjects. In addition, in vitro study was done to determine the production of the two cytokines and index of apoptosis and oxidative injuries in human kidney epithelial cells (HK-2) exposed to three high levels of calcium. Data showed that both urinary MCP-1 and HMGB1 in group CN were higher than that of group C. When the patients were subdivided, comparisons among the three groups showed that both MCP-1 and HMGB1 in group H and group N were higher than group C, but there was no significant statistical difference between the two stone groups. In vitro study, the apoptosis rate of cells, the lactate dehydrogenase activities, the hydrogen peroxide, and 8-isoprostane concentrations in the medium all increased in accordance with the increased concentration of calcium supplemented. Compared with the control, mRNA expressions of MCP-1 and HMGB1 in cells and the protein concentrations of the two cytokines in the medium of calcium-supplemented groups increased significantly. Results showed that urinary MCP-1 and HMGB1 increased in calcium nephrolithiasis patients and hypercalciuria might affect the identical pathways (through the reactive oxygen species) with other factors in stimulating the production of MCP-1 and HMGB1 in vivo.

Kidney stones

Kidney stones are mineral deposits in the renal calyces and pelvis that are found free or attached to the renal papillae. They contain crystalline and organic components and are formed when the urine becomes supersaturated with respect to a mineral. Calcium oxalate is the main constituent of most stones, many of which form on a foundation of calcium phosphate called Randall's plaques, which are present on the renal papillary surface. Stone formation is highly prevalent, with rates of up to 14.8% and increasing, and a recurrence rate of up to 50% within the first 5 years of the initial stone episode. Obesity, diabetes, hypertension and metabolic syndrome are considered risk factors for stone formation, which, in turn, can lead to hypertension, chronic kidney disease and end-stage renal disease. Management of symptomatic kidney stones has evolved from open surgical lithotomy to minimally invasive endourological treatments leading to a reduction in patient morbidity, improved stone-free rates and better quality of life. Prevention of recurrence requires behavioural and nutritional interventions, as well as pharmacological treatments that are specific for the type of stone. There is a great need for recurrence prevention that requires a better understanding of the mechanisms involved in stone formation to facilitate the development of more-effective drugs.

Role of mitochondria and NADPH oxidase derived reactive oxygen species in hyperoxaluria induced nephrolithiasis: therapeutic intervention with combinatorial therapy of N-acetyl cysteine and Apocynin

The interactions between the main cellular sources of ROS, such as mitochondria and NADPH oxidase, are known to play an imperative role in the pathogenesis of hyperoxaluria-induced nephrolithiasis. The present study was designed to investigate the protective effect of a combinatorial therapy based on the attenuation of oxidative stress with antioxidant (N-acetyl cysteine), and NADPH oxidase inhibitor (apocynin), that might be required to effectively eliminate hyperoxaluric manifestations. Hyperoxaluria was induced in male Wistar rats by administering 0.4% ethylene glycol with 1% ammonium chloride in drinking water for 9 days. Hyperoxaluria accentuated renal oxidative stress in terms of increased ROS production and lipid peroxidation. Mitochondrial dysfunction, a central deleterious event in renal stone crystallization, was evident by decreased activities of electron transport chain complex I, II and IV, augmented mitochondrial ROS, reduced GSH/GSSG ratio, which resulted in the mitochondrial permeability transition pore (mPTP) opening as indicated by increased mitochondrial swelling in hyperoxaluric rats. Furthermore, NADPH oxidase activity was significantly increased, with raised expression of NOX1, NOX2, NOX4, p38MAPK and MnSOD, in the renal tissue of hyperoxaluric rats compared to control. However, combinatorial therapy with N-acetyl cysteine (50mg/kg/day) and apocynin (200mg/kg/day), intraperitoneally, significantly improved renal functions in hyperoxaluric rats and considerably ameliorated mitochondrial dysfunction. NAC with apocynin was also found to be effective in reducing the redundant activity of NADPH oxidase in renal tissue of hyperoxaluric rats. Hence, our investigation provides novel mechanistic insights that combinatorial approaches using targeted modulators of ROS offer therapeutic benefits in hyperoxaluria-induced nephrolithiasis.

Osteogenic changes in kidneys of hyperoxaluric rats

Many calcium oxalate (CaOx) kidney stones develop attached to renal papillary sub-epithelial deposits of calcium phosphate (CaP), called Randall's plaque (RP). Pathogenesis of the plaques is not fully understood. We hypothesize that abnormal urinary environment in stone forming kidneys leads to epithelial cells losing their identity and becoming osteogenic. To test our hypothesis male rats were made hyperoxaluric by administration of hydroxy-l-proline (HLP). After 28days, rat kidneys were extracted. We performed genome wide analyses of differentially expressed genes and determined changes consistent with dedifferentiation of epithelial cells into osteogenic phenotype. Selected molecules were further analyzed using quantitative-PCR and immunohistochemistry. Genes for runt related transcription factors (RUNX1 and 2), zinc finger protein Osterix, bone morphogenetic proteins (BMP2 and 7), bone morphogenetic protein receptor (BMPR2), collagen, osteocalcin, osteonectin, osteopontin (OPN), matrix-gla-protein (MGP), osteoprotegrin (OPG), cadherins, fibronectin (FN) and vimentin (VIM) were upregulated while those for alkaline phosphatase (ALP) and cytokeratins 10 and 18 were downregulated. In conclusion, epithelial cells of hyperoxaluric kidneys acquire a number of osteoblastic features but without CaP deposition, perhaps a result of downregulation of ALP and upregulation of OPN and MGP. Plaque formation may additionally require localized increases in calcium and phosphate and decrease in mineralization inhibitory potential.

Involvement of renin-angiotensin-aldosterone system in calcium oxalate crystal induced activation of NADPH oxidase and renal cell injury

INTRODUCTION AND OBJECTIVES

Reactive oxygen species (ROS) are produced during the interaction between oxalate/calcium oxalate monohydrate (COM) crystals and renal epithelial cells and are responsible for the various cellular responses through the activation of NADPH oxidase (Nox). Ox and COM also activate the renin-angiotensin-aldosterone system (RAAS). Aldosterone stimulates ROS production through activation of Nox with the involvement of mineralocorticoid receptor (MR), Rac1 and mitogen-activated protein kinases (MAPK). We investigated RAAS pathways in vivo in an animal model of hyperoxaluria and in vitro by exposing renal epithelial cells to COM crystals.

METHODS

Hyperoxaluria was induced in male SD rats by administering ethylene glycol. One group of rats was additionally given spironolactone. Total RNA was extracted and subjected to genomic microarrays to obtain global transcriptome data. Normal rat kidney cell line (NRK-52E) was incubated with aldosterone(10(-7) M) and COM(67 μg/cm(2)) with or without spironolactone(10(-5) M), a selective inhibitor of SRC family of kinases; protein phosphatase 2(pp2) (10(-5) M) and Nox inhibitor; diphenylene iodonium (DPI) (10(-5) M).

RESULTS

Relative expression of genes encoding for AGT, angiotensin receptors 1b and 2, Renin 1, Cyp11b, HSD11B2, Nr3c2, NOx4 and Rac1 was upregulated in the kidneys of rats with hyperoxaluria. Treatment with spironolactone reversed the effect of hyperoxaluria. Both aldosterone and COM crystals activated Nox and Rac1 expression in NRK52E, while spironolactone inhibited Nox and Rac1 expression. Increased Rac1 expression was significantly attenuated by treatment with PP2 and spironolactone.

CONCLUSIONS

Results indicate that hyperoxaluria-induced production of ROS, injury and inflammation are in part associated with the activation of Nox through renin-angiotensin-aldosterone pathway.

Sodium thiosulfate ameliorates oxidative stress and preserves renal function in hyperoxaluric rats

Background

Hyperoxaluria causes crystal deposition in the kidney, which leads to oxidative stress and to injury and damage of the renal epithelium. Sodium thiosulfate (STS, Na₂S₂O₃) is an anti-oxidant, which has been used in human medicine for decades. The effect of STS on hyperoxaluria-induced renal damage is not known.

Methods

Hyperoxaluria and renal injury were induced in healthy male Wistar rats by chronic exposure to ethylene glycol (EG, 0.75%) in the drinking water for 4 weeks. The treatment effects of STS, NaCl or Na₂SO₄ were compared. Furthermore, the effects of STS on oxalate-induced oxidative stress were investigated in vitro in renal LLC-PK1 cells.

Results

Chronic EG exposure led to hyperoxaluria, oxidative stress, calcium oxalate crystalluria and crystal deposition in the kidneys. Whereas all tested compounds significantly reduced crystal load, only STS-treatment maintained tissue superoxide dismutase activity and urine 8-isoprostaglandin levels in vivo and preserved renal function. In in vitro studies, STS showed the ability to scavenge oxalate-induced ROS accumulation dose dependently, reduced cell-released hydrogen peroxide and preserved superoxide dismutase activity. As a mechanism explaining this finding, STS was able to directly inactivate hydrogen peroxide in cell-free experiments.

Conclusions

STS is an antioxidant, which preserves renal function in a chronic EG rat model. Its therapeutic use in oxidative-stress induced renal-failure should be considered.

Nox and renal disease

Since the first demonstration of Nox enzyme expression in the kidney in the early 1990s and the subsequent identification of Nox4, or RENOX, a decade later, it has become apparent that the Nox family of reactive oxygen species (ROS) generating enzymes plays an integral role in the normal physiological function of the kidney. As our knowledge of Nox expression patterns and functions in various structures and specialized cell types within the kidney grows, so does the realization that Nox-derived oxidative stress contributes significantly to a wide variety of renal pathologies through their ability to modify lipids and proteins, damage DNA and activate transcriptional programmes. Diverse studies demonstrate key roles for Nox-derived ROS in kidney fibrosis, particularly in settings of chronic renal disease such as diabetic nephropathy. As the most abundant Nox family member in the kidney, much emphasis has been placed on the role of Nox4 in this setting. However, an ever growing body of work continues to uncover key roles for other Nox family members, not only in diabetic kidney disease, but in a diverse array of renal pathological conditions. The objective of the present review is to highlight the latest novel developments in renal Nox biology with an emphasis not only on diabetic nephropathy but many of the other renal disease contexts where oxidative stress is implicated.

Inhalation of hydrogen gas ameliorates glyoxylate-induced calcium oxalate deposition and renal oxidative stress in mice

The aim of this study is to evaluate the protective effect and underlying mechanism of hydrogen gas (H2) to glyoxylate induced renal calcium oxalate (CaOx) crystal deposition in mice. In present work, rodent renal CaOx crystal deposition model was introduced by intra-abdominal injection of glyoxylate (100 mg/kg/d) for 5 days. Two days before administration of glyoxylate, inhalation of H2 for 30 min per day was initiated and continued for 7 days. By the end of the study, the samples of 24 hours urine, serum and renal tissue were collected for biochemical and pathological assay. According to levels of urine calcium excretion, renal calcium deposition, a serum excretion of kidney injury molecule-1 (KIM-1) assay and a TUNEL assay, inhalation of H2 could successfully decrease the CaOx crystallizations and protect against renal injury. Crystal deposition in the kidneys is associated with oxidative stress, which was indicated by increased levels of renal malondialdehyde (MDA) and 8-hydroxydeoxyguanosine (8-OHdG) and decreased activities of superoxide dismutase (SOD), glutathione (GSH) and catalase (CAT). These effects were reversed by a high-dose H2 pretreatment. The renal expressions of osteopontin (OPN), CD44, monocyte chemoattractant protein-1 (MCP-1) and interleukin-10 (IL-10) were markedly increased in glyoxylate-treated mice, and H2 significantly attenuated the increase of OPN, CD44 and MCP-1 but upregulated the expression of IL-10. Our findings demonstrate that inhalation of H2 reduces renal crystallization, renal oxidative injury and inflammation and it may be a candidate agent with few adverse effects for prevention of nephrolithiasis.

Enteric hyperoxaluria: an important cause of end-stage kidney disease

Hyperoxaluria is a frequent complication of inflammatory bowel diseases, ileal resection and Roux-en-Y gastric bypass and is well-known to cause nephrolithiasis and nephrocalcinosis. The associated prevalence of chronic kidney disease and end-stage kidney disease (ESKD) is less clear but may be more consequential than recognized. In this review, we highlight three cases of ESKD due to enteric hyperoxaluria following small bowel resections. We review current information on the pathophysiology, complications and treatment of this complex disease.

Activation of the NLRP3 inflammasome in association with calcium oxalate crystal induced reactive oxygen species in kidneys

PURPOSE

We investigated the association of hyperoxaluria and calcium oxalate crystal induced production of reactive oxygen species with activation of the NLRP3 inflammasome.

MATERIALS AND METHODS

Eight-week-old male rats were given hydroxy-L-proline to induce hyperoxaluria. A group of rats on the hydroxy-L-proline diet also received apocynin, an antioxidant and nonspecific inhibitor of NADPH oxidase. At 28 days the rats were sacrificed and the kidneys were extracted. Microarray analysis was done with the BeadArray™ Reader. Gene ontology and gene pathway analyses were done with the DAVID (Database for Annotation, Visualization of Integrated Discovery) enrichment analysis tool. Quantitative real-time polymerase chain reaction and immunohistochemical staining were performed to confirm microarray results.

RESULTS

Analysis of 22,226 genes revealed that 20 and 24 pathways were highly significant in the cortex and medulla, respectively. In the cortex extracellular matrix-receptor interaction, complement and coagulation cascades, focal adhesion and hypertrophic cardiomyopathy were the most significant pathways. In the medulla complement and coagulation cascades, extracellular matrix-receptor interaction and dilated cardiomyopathy were the major pathways. Genes encoding for PYCARD (ASC), TXNIP, NLRP3, caspase-1, and IL-1β and 18 were significantly up-regulated in hydroxy-L-proline fed rats but in the group that received apocynin these genes were down-regulated in the cortex and medulla. Results were verified by quantitative real-time polymerase chain reaction with SYBR® Green assay and immunohistochemical staining.

CONCLUSIONS

Results indicate a role for reactive oxygen species in activation of the NLRP3 inflammasome via TXNIP. This led to a robust inflammatory response in the kidneys of rats with hyperoxaluria and calcium oxalate nephrolithiasis.

The selective NADPH oxidase inhibitor apocynin has potential prophylactic effects on melamine-related nephrolithiasis in vitro and in vivo

The objective of this study is to examine the effects of apocynin on melamine-cyanuric acid mixture (MCM)-induced nephrolithiasis in vitro and in vivo. For the in vitro experiments, changes in oxidative stress (OS) markers and the expression of osteopontin (OPN) and phospho-p38 (p-p38) were measured to assess the effects of apocynin treatment after MCM-induced crystallization in HK-2 cells, a human renal epithelial-derived cell line. For in vivo studies, the potential effects of apocynin in preventing and treating nephrolithiasis were analyzed with a MCM-induced nephrolithiasis rat model, and urea and creatinine levels were measured. Urinary 8-IP (a product of lipid peroxidation) and malondialdehyde levels and superoxide dismutase activity were assessed in the kidneys as markers of renal OS. The kidneys were removed, weighed, and subjected to histopathological examination. The urolithiasis-associated proteins p-p38 and OPN were evaluated by immunohistochemistry and Western blotting. Apocynin treatment prevented the MCM-induced changes in OS and in OPN and p-p38 expression in HK-2 cells. For in vivo experiments, the expression of OS markers, renal OPN, and p-p38 increased after MCM administration, and these increases were diminished by apocynin. In addition, apocynin prevented MCM-induced renal crystallization. Moreover, prophylactic apocynin treatment reduced MCM-induced nephrotoxicity. After therapeutic apocynin treatment in nephrolithic rats, OS decreased, but the other indicators did not improve significantly. Prophylactic apocynin administration reduced renal melamine-related-crystal deposition, potentially by modulating OS and thereby decreasing p-p38 and OPN expression.

Therapeutic effect of Xue Niao An on glyoxylate-induced calcium oxalate crystal deposition based on urinary metabonomics approach

The anti-nephrolithiasis effect of Xue Niao An (XNA) capsules is explored by analyzing urine metabolic profiles in mouse models, with ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). An animal model of calcium oxalate crystal renal deposition was established in mice by intra-abdominal injection of glyoxylate. Then, treatment with XNA by intra-gastric administration was performed. At the end of the study, calcium deposition in kidney was measured by Von Kossa staining under light microscopy, and the Von Kossa staining changes showed that XNA significantly alleviated the calcium oxalate crystal deposition. Meanwhile, urine samples for fifteen metabolites, including amino acids and fatty acids, with significant differences were detected in the calcium oxalate group, while XNA treatment attenuated metabolic imbalances. Our study indicated that the metabonomic strategy provided comprehensive insight on the metabolic response to XNA treatment of rodent renal calcium oxalate deposition.